This invention relates to apparatus for data transfer with a replaceable, rotating magnetic disk, particularly a flexible magnetic disk which normally is packaged in cartridge form. More particularly, the invention pertains to a system for saving power consumed by a disk sensor incorporated in such rotating disk data storage apparatus for sensing the loading and unloading of a disk, or a disk cartridge, in and from the apparatus.
Various power saving schemes have been suggested and used with floppy disk drives. Among such conventional suggestions is that described and claimed in U.S. Pat. No. 4,658,307 filed by Tsuyuguchi et al. and assigned to the assignee of the instant application. Tsuyuguchi et is al. teaches to connect the disk motor drive circuit, head motor drive circuit and read/write circuit, all standard components of the disk drive, to a power supply via a power saving switch. This switch is closed only when a disk sensor, another standard component, senses the loading of the floppy disk cartridge in the disk drive, or when the "drive select" and "motor on" signals from the host system, under which control the disk drive operates, are in prescribed states. The motor drive circuits and read/write circuit are therefore not powered in the absence of the disk cartridge, or when the "drive select" and "motor on" signals are in other than the prescribed states, even if the complete data processing system, comprising the host and one or more disk drives, is powered on. A very substantial saving of power can thus be accomplished.
As far as the applicant is aware, however, no power saving measure was conventionally taken for the disk sensor itself. In exploring the possibilities of reducing the waste of power by the disk sensor, the applicant has paid attention to the information that is contained in control an data fed from some host systems and which indicates whether the disk as drive is active or inactive, that is, whether the disk drive is to be, or being, put to reading or writing, or is just standing by. This information will be hereinafter referred to as the power save signal as various power consuming components of the disk drive have proved to be capable of being held unpowered when the signal indicates standby.
The trouble with the disk sensor is that it is totally unpredictable just when the disk will be loaded in, and unloaded from, the disk drive, the loading and unloading of the disk being purely at the will of the user. Whenever the disk was unloaded, the disk sensor circuit of conventional design immediately signaled the host system to that effect. For this reason a voltage was held applied to the disk sensor as long as the data processing system was powered on.
Consider a disk sensor circuit comprising a serial connection of a sensor switch, which is turned on or off depending upon whether the disk is loaded in or unloaded from the disk drive, and a resistor. A current flowed through the resistor as long as the sensor switch remained closed, as when the disk was not loaded, with the consequent loss of power. Now that the power requirements of other power consuming parts of the disk drive have been reduced to a minimum, and with the advent of battery powered disk drives, the saving of power consumed by the disk sensor has become imperative in view of strong, consistent demands from the users for less power consuming disk drives.